T-cell mediated rejection of gene-modified HIV-specific cytotoxic T lymphocytes in HIV-infected patients

Gene therapy and dermatology: more than just skin deep

BACKGROUND

Recent advances in the molecular characterization of dermatologic disease have substantively augmented the understanding of the pathogenetic processes underlying disorders of the skin. This new knowledge coupled with progress in gene delivery technologies has paved the way for introducing cutaneous gene therapy into the dermatologic therapeutic armamentorium.

OBJECTIVE

This review article includes an overview of the current strategies for delivery of gene therapy with an emphasis on the potential role of cutaneous gene delivery in the treatment of skin and systemic diseases.

CONCLUSIONS

Accessibility for gene delivery, clinical evaluation, and topical modulation of gene expression render the skin a very attractive tissue for therapeutic gene delivery. However, there are several key hurdles to be overcome before cutaneous gene therapy becomes a viable clinical option. These include difficulties in inducing sustained expression of the desired gene in vivo, the challenge of targeting genes to long-lived stem cells, and the difficulty in achieving specific and uniform transfer to different compartments of the skin. However, these problems are not insurmountable and will likely be resolved in conjunction with ongoing advances in delineating gene expression profiles and other molecular properties of the skin, strategies for stem cell isolation, and improved approaches to regulating gene delivery and expression. These advances should create the framework for translating the enormous potential of cutaneous gene therapy into the clinical arena and, thereby, substantively improving the management of both cutaneous and systemic disease.

Genetic regulatory elements introduced into neural stem and progenitor cell populations

The genetic manipulation of neural cells has advantage in both basic biology and medicine. Its utility has provided a clearer understanding of how the survival, connectivity, and chemical phenotype of neurones is regulated during, and after, embryogenesis. Much of this achievement has come from the recent generation by genetic means of reproducible and representative supplies of precursor cells which can then be analyzed in a variety of paradigms. Furthermore, advances made in the clinical use of transplantation for neurodegenerative disease have created a demand for an abundant, efficacious and safe supply of neural cells for grafting. This review describes how genetic methods, in juxtaposition to epigenetic means, have been used advantageously to achieve this goal. In particular, we detail how gene transfer techniques have been developed to enable cell immortalization, manipulation of cell differentiation and commitment, and the controlled selection of cells for purification or safety purposes. In addition, it is now also possible to genetically modify antigen presentation on cell surfaces. Finally, there is detailed the transfer of therapeutic products to discrete parts of the central nervous system (CNS), using neural cells as elegant and sophisticated delivery vehicles. In conclusion, once the epigenetic and genetic controls over neural cell production, differentiation and death have been more fully determined, providing a mixture of hard-wired elements and more flexibly expressed characteristics becomes feasible. Optimization of the contributions and interactions of these two controlling systems should lead to improved cell supplies for neurotransplantation.

Immune response to green fluorescent protein: implications for gene therapy

Green fluorescent protein (GFP) is a widely used intracellular reporter molecule to assess gene transfer and expression. A potential use for GFP is as a co-expressed marker, to select and enrich gene-modified cells by flow cytometry. Processed peptides derived from GFP and presented by the major histocompatibility complex on the cell surface could potentially induce T cell immune responses against GFP+ cells. Thus, clinical application of GFP is premature, since in vivo studies on its immunogenicity are lacking. Therefore, we investigated immune responses against EGFP (enhanced-GFP) in two transplantable murine models: the BALB/c (H-2d) BM185 pre-B leukemia and the C57BL/6 (H-2b) EL-4 T cell lymphoma. BM185 and EL-4 cell lines modified to express high levels of EGFP showed drastic reduction of disease development when transplanted into immunocompetent mice. BM185/ EGFP did lead to rapid development of disease in immunodeficient Nu/Nu mice. Mice surviving BM185/EGFP leukemia challenge developed high cytotoxic T lymphocyte (CTL) responses against EGFP-expressing cells. Furthermore, immune stimulation against BM185/EGFP cells could also be induced by immunization with EGFP+ transduced dendritic cells. The effects of the co-expression of EGFP and immunomodulators (CD80 plus GM-CSF) were also investigated as an irradiated leukemia vaccine. EGFP co-expression by the vaccine did not interfere with the development of CTLs against the parental leukemia or with the anti-leukemia response in vivo. These results indicate that the immune response against EGFP may interfere with its applicability in gene insertion/replacement strategies but could potentially be employed for leukemia cell vaccines.

Rapid titer determination using quantitative real-time PCR

Quantitative real-time PCR was utilized to evaluate retroviral vector titer. RNA was prepared from vector supernatant and run in a one-step RT-PCR reaction combining reverse transcription (RT) and amplification in one tube. Sample analysis was performed in the ABI Prism 7700 Sequence Detector. PCR was quantitative over a range of 101 to 6 x 105 vector particles per reaction (2 x 102 to 1 x 107 vector particles per millilites of supernatant) and closely corre- lated with biologic titers performed on the test material. The 96-well capacity of the machine and 2 h of running time permit titer determinations within 8 h, facilitating the processing of large sample numbers while greatly decreasing technician time. Real-time PCR improves titer quantification and the identification of high-titer producer cells. This methodology will help investigators meet the challenges of developing vectors which lack selectable markers.

Natural killer cell-mediated lysis of autologous cells modified by gene therapy

This study investigated the role of natural killer (NK) cells as effectors of an immune response against autologous cells modified by gene therapy. T lymphocytes were transduced with LXSN, a retroviral vector adopted for human gene therapy that carries the selectable marker gene neo, and the autologous NK response was evaluated. We found that (i) infection with LXSN makes cells susceptible to autologous NK cell-mediated lysis; (ii) expression of the neo gene is responsible for conferring susceptibility to lysis; (iii) lysis of neo-expressing cells is clonally distributed and mediated only by NK clones that exhibit human histocompatibility leukocyte antigen (HLA)-Bw4 specificity and bear KIR3DL1, a Bw4-specific NK inhibitory receptor; and (iv) the targets are cells from HLA-Bw4(+) individuals. Finally, neo peptides anchoring to the Bw4 allele HLA-B27 interfered with KIR3DL1-mediated recognition of HLA-B27, i.e., they triggered NK lysis. Moreover, neo gene mutations preventing translation of two of the four potentially nonprotective peptides reduced KIR3DL1(+) NK clone-mediated autologous lysis. Thus, individuals expressing Bw4 alleles possess an NK repertoire with the potential to eliminate autologous cells modified by gene therapy. By demonstrating that NK cells can selectively detect the expression of heterologous genes, these observations provide a general model of the NK cell-mediated control of viral infections.

Inhibition of human immunodeficiency virus type 1 replication in vitro in acutely and persistently infected human CD4+ mononuclear cells expressing murine and humanized anti-human immunodeficiency virus type 1 Tat single-chain variable fragment intrabodies

We have previously reported that a murine anti-Tat sFv intrabody, termed sFvtat1Ck, directed against the proline-rich N-terminal activation domain of HIV-1, is a potent inhibitor of HIV-1 replication [Mhashilkar, A. M., et al. (1995). EMBO J. 14, 1542-1551]. In this study, the protective effect of sFvtat1Ck expression on HIV-1 replication in both acutely infected and persistently infected CD4+ cells was examined. Stably transfected CD4+ SupT1 cells were resistant to HIV-1 infection at high MOI with both the laboratory isolate HxB2 and six syncytium-inducing (SI) primary isolates. Persistently infected U1 cells, which can be induced to increase HIV-1 mRNA synthesis on addition of PMA or TNF-alpha, showed decreased production of HIV-1 in the presence of sFvtat1Ck. In transduced CD4+-selected, CD8+-depleted, and total PMBCs, the sFvtat1Ck-expressing cells showed marked inhibition of HIV-1 replication. The anti-Tat sFv was subsequently humanized by substituting compatible human framework regions that were chosen from a large database of human V(H) and V(L) sequences on the basis of high overall framework matching, similar CDR length, and minimal mismatching of canonical and V(H)/V(L) contact residues. One humanized anti-Tat sFv intrabody, termed sFvhutat2, demonstrated a level of anti-HIV-1 activity that was comparable to the parental murine sFv when transduced PBMCs expressing the murine or humanized sFv intrabodies were challenged with HxB2 and two SI primary isolates. Because Tat is likely to have both direct and indirect effects in the pathogenesis of AIDS through its multiple roles in the HIV-1 life cycle and through its effects on the immune system, the strategy of genetically blocking Tat protein function with a humanized anti-Tat sFv intrabody may prove useful for the treatment of HIV-1 infection and AIDS, particularly when used as an adjuvant gene therapy together with highly active antiretroviral therapies that are currently available.

Sustained gene expression in transplanted skin fibroblasts in rats

Retrovirus-mediated gene transfer into adult skin fibroblasts has provided measurable amounts of therapeutic proteins in animal models. However, the major problem emerging from these experiments was a limited time of vector encoded gene expression once transduced cells were engrafted. We hypothesized that sustained transduced gene expression in quiescent fibroblasts in vivo might be obtained by using a fibronectin (Fn) promoter. Fibronectin plays a key role in cell adhesion, migration and wound healing and is up-regulated in quiescent fibroblasts. Retroviral vectors containing human adenosine deaminase (ADA) cDNA linked to rat fibronectin promoter (LNFnA) or viral LTR promoter (LASN) were compared for their ability to express ADA from transduced primary rat skin fibroblasts in vivo. Skin grafts formed from fibroblasts transduced with LNFnA showed strong human ADA enzyme activity from 1 week to 3 months. In contrast, skin grafts containing LASN-transduced fibroblasts tested positive for human ADA for weeks 1 and 2, were faintly positive at week 3 and showed no human ADA expression at 1, 2 and 3 months. Thus, a fibronectin promoter provided sustained transduced gene expression at high levels for at least 3 months in transplanted rat skin fibroblasts, perhaps permitting the targeting of this tissue for human gene therapy.

Gene therapy of glioblastoma multiforme via combined expression of suicide and cytokine genes: a pilot study in humans

Retrovirus-mediated gene therapy is a particularly attractive approach for glioblastoma multiforme (GBM), given the poor prognosis of this tumour and its localized proliferation in post-mitotic tissue. In this study we assessed, for the first time in humans, the therapeutic potential of a newly designed bicistronic Moloney vector (pLIL-2-TK), combining the expression of a suicide gene (thymidine kinase, tk) with an immunomodulatory gene (human interleukin 2, IL-2). Evidence of transgene activity in the treated tumours is presented.

No discrepancy between in vivo gene marking efficiency assessed in peripheral blood populations compared with bone marrow progenitors or CD34+ cells

Reports of 1- to 2-log higher gene transfer levels in purified CD34+ cells or marrow CFU compared with levels in mature circulating blood cells after transplantation of retrovirally transduced primitive human hematopoietic cells have resulted in concern that transduced progenitors do not contribute proportionally to ongoing hematopoiesis (Kohn et al., 1995; Brenner, 1996). To study the issue in a relevant large animal, we analyzed samples of mature blood cells, marrow CD34-enriched cells and marrow CD34-depleted cells, and marrow CFU from a cohort of 11 rhesus transplanted with retrovirally transduced cells and followed for up to 5.5 years. They were transplanted with CD34-enriched bone marrow (BM) or G-CSF/SCF-mobilized peripheral blood (PB) cells transduced with vectors containing either neo, human glucocerebrosidase, or murine adenosine deaminase genes. There were no significant differences between the levels of vector sequences found in BM CD34+ cells, BM CD34- cells, PB granulocytes, or PB mononuclear cells (MNCs) in any animal. In four animals transplanted with SCF/G-CSF-primed BM cells and analyzed 3-6 months posttransplantation, the percentage of CFU containing the neo vector appeared to be 1 log higher than the representation of marked cells in the PB of these animals, but this discrepancy did not persist at time points greater than 6 months posttransplantation. The level of CFU marking was no higher than PB granulocyte or MNC marking at any time points in the other animals. Low levels of mature gene-modified cells probably reflect poor transduction of repopulating stem cells, not a block in differentiation or specific immune rejection of mature cells. This study represents the longest follow-up of primates transplanted with transduced hematopoietic cells, and it is encouraging that the levels of vector-containing cells appear stable for up to 5 years.

Rapid Death of Adoptively Transferred T Cells in Acquired Immunodeficiency Syndrome

Human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes (CTL) probably play the major role in controlling HIV replication. However, the value of adoptive transfer of HIV-specific CTL expanded in vitro to HIV+ patients has been limited: this contrasts with the success of CTL therapy in treating or preventing Epstein-Barr virus and cytomegalovirus disease after bone marrow transplantation (BMT). We investigated the fate of expanded HIV-specific CTL clones in vivo following adoptive transfer to a patient with acquired immunodeficiency syndrome (AIDS). Two autologous CTL clones specific for HIV Gag and Pol were expanded to large numbers (>109) in vitro and infused into an HIV-infected patient whose viral load was rising despite antiretroviral therapy. The fate of one clone was monitored by staining peripheral blood mononuclear cells (PBMCs) with T-cell receptor–specific tetrameric major histocompatibility complex (MHC)-peptide complexes. Although the CTL transfer was well tolerated, there were no significant changes in CD4 and CD8 lymphocyte counts and virus load. By tracking an infused clone using soluble MHC-peptide complexes, we show that cells bearing the Gag-specific T-cell receptors were rapidly eliminated within hours of infusion through apoptosis. Thus, the failure of adoptively transferred HIV-specific CTL to reduce virus load in AIDS may be due to rapid apoptosis of the infused cells, triggered by a number of potential mechanisms. Further trials of adoptive transfer of CTL should take into account the susceptibility of infused cells to in vivo apoptosis.

Rapid Death of Adoptively Transferred T Cells in Acquired Immunodeficiency Syndrome

Human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes (CTL) probably play the major role in controlling HIV replication. However, the value of adoptive transfer of HIV-specific CTL expanded in vitro to HIV+ patients has been limited: this contrasts with the success of CTL therapy in treating or preventing Epstein-Barr virus and cytomegalovirus disease after bone marrow transplantation (BMT). We investigated the fate of expanded HIV-specific CTL clones in vivo following adoptive transfer to a patient with acquired immunodeficiency syndrome (AIDS). Two autologous CTL clones specific for HIV Gag and Pol were expanded to large numbers (>109) in vitro and infused into an HIV-infected patient whose viral load was rising despite antiretroviral therapy. The fate of one clone was monitored by staining peripheral blood mononuclear cells (PBMCs) with T-cell receptor–specific tetrameric major histocompatibility complex (MHC)-peptide complexes. Although the CTL transfer was well tolerated, there were no significant changes in CD4 and CD8 lymphocyte counts and virus load. By tracking an infused clone using soluble MHC-peptide complexes, we show that cells bearing the Gag-specific T-cell receptors were rapidly eliminated within hours of infusion through apoptosis. Thus, the failure of adoptively transferred HIV-specific CTL to reduce virus load in AIDS may be due to rapid apoptosis of the infused cells, triggered by a number of potential mechanisms. Further trials of adoptive transfer of CTL should take into account the susceptibility of infused cells to in vivo apoptosis.

Macaque lymphocytes transduced by a constitutively expressed interferon beta gene display an enhanced resistance to SIVmac251 infection

We are developing a method of gene therapy of HIV infection based on the low constitutive expression of an interferon beta (IFN-beta) gene in HIV target cells. Herein we report the first step in the development of a relevant animal model, provided by the macaque (Macaca fascicularis) infected with a pathogenic SIVmac251 isolate. To avoid the possibility of in vivo rejection of macaque lymphocytes expressing Hu IFN-beta, we have PCR-amplified and sequenced the Ma IFN-beta-coding sequence, and placed it under the control of a PstI-NruI 0.6-kb fragment of the murine H-2Kb gene promoter in the MFG-K(b)MaIFNbeta retroviral vector. Lymphocytic CEMX174 cells, transduced by coculture on packaging cells with this construct, harbored a mean of 0.07 to 1.2 copies of the IFN-beta transgene per cell, and were characterized by an IFN production ranging from 75 to 750 units per 5 x 10(5) cells per 3 days. The IFN-beta-transduced populations displayed an enhanced resistance against the pathogenic SIVmac251 isolate. Control experiments showed that the enhanced resistance could not be ascribed to the Ma IFN-beta released during the 3 days of coculture by the packaging cells, or to the mere transduction with a retroviral vector. Macaque lymphocytes transduced by the MFG-K(b)MaIFNbeta retroviral vector by coculture on packaging cells, acquired a mean number of IFN-beta transgene copies per cell ranging from 0.03 to 0.1. Such transduction led to the release of IFN-beta into the culture medium, ranging from 10 to 20 units per 5 x 10(5) cells per 3 days. This increased the anti-SIV resistance of the lymphocytes, as demonstrated by a decreased p27 antigen release into the culture medium, without affecting lymphocyte proliferation.

In pursuit of new developments for gene therapy of human diseases

Gene therapy aims at transferring a therapeutic gene into human somatic cells in order to treat a disease. Originally addressed to hereditary genetic disorders, gene therapy has found therapeutic applications in cancer, infectious diseases and degenerative disorders, particularly those of the nervous system. Although gene transfer into humans has been demonstrated in several clinical trials, with more than 300 currently underway worldwide, there is still no single outcome that undoubtedly showed a consistent benefit for the patient. Nevertheless, the expectations for gene therapy are still high, and the prospects of future clinical success are increasing together with the growing of the field. The development of better delivery systems specifically tailored to individual diseases, with sustained expression of the therapeutic gene in the appropriate cells, will in the end make possible true therapeutic applications of human gene transfer.

Safety and biological efficacy of an adeno-associated virus vector-cystic fibrosis transmembrane regulator (AAV-CFTR) in the cystic fibrosis maxillary sinus

OBJECTIVE

The host immune response and low vector efficiency have been key impediments to effective cystic fibrosis transmembrane regulator (CFTR) gene transfer for cystic fibrosis (CF). An adeno-associated virus vector (AAV-CFTR) was used in a phase I dose-escalation study to transfer CFTR cDNA into respiratory epithelial cells of the maxillary sinus of 10 CF patients.

STUDY DESIGN

A prospective, randomized, unblinded, dose-escalation, within-subjects, phase I clinical trial of AAV-CFTR was conducted.

PATIENTS

Ten patients with previous bilateral maxillary antrostomies were treated.

MAIN OUTCOME MEASURES

Safety, gene transfer as measured by semiquantitative polymerase chain reaction (PCR), and sinus transepithelial potential difference (TEPD) were measured.

RESULTS

The highest level of gene transfer was observed in the range of 0.1-1 AAV-CFTR vector copy per cell in biopsy specimens obtained 2 weeks after treatment. When tested, persistence was observed in one patient for 41 days and in another for 10 weeks. Dose-dependent changes in TEPD responses to pharmacologic intervention were observed following treatments. Little or no inflammatory or immune responses were observed.

CONCLUSION

AAV-CFTR administration to the maxillary sinus results in successful, dose-dependent gene transfer to the maxillary sinus and alterations in sinus TEPD suggestive of a functional effect, with little or no cytopathic or host immune response. Further study is warranted for AAV vectors as they may prove useful for CFTR gene transfer and other in vivo gene transfer therapies. A prospective, randomized, double-blind, placebo-controlled, within-subjects, phase II clinical trial of the effect AAV-CFTR on clinical recurrence of sinusitis will determine the clinical efficacy of AAV gene therapy for CF.

Anti-tumor activity of human T cells expressing the CC49-zeta chimeric immune receptor

A chimeric immune receptor consisting of an extracellular antigen-binding domain derived from the CC49 humanized single-chain antibody, linked to the CD3zeta signaling domain of the T cell receptor, was generated (CC49-zeta). This receptor binds to TAG-72, a mucin antigen expressed by most human adenocarcinomas. CC49-zeta was expressed in CD4+ and CD8+ T cells and induced cytokine production on stimulation. Human T cells expressing CC49-zeta recognized and killed tumor cell lines and primary tumor cells expressing TAG-72. CC49-zeta T cells did not mediate bystander killing of TAG-72-negative cells. In addition, CC49-zeta T cells not only killed FasL-positive tumor cells in vitro and in vivo, but also survived in their presence, and were immunoprotective in intraperitoneal and subcutaneous murine tumor xenograft models with TAG-72-positive human tumor cells. Finally, receptor-positive T cells were still effective in killing TAG-72-positive targets in the presence of physiological levels of soluble TAG-72, and did not induce killing of TAG-72-negative cells under the same conditions. This approach is being currently being utilized in a phase I clinical trial for the treatment of colon cancer.

Single cell analysis and selection of living retrovirus vector-corrected mucopolysaccharidosis VII cells using a fluorescence-activated cell sorting-based assay for mammalian beta-glucuronidase enzymatic activity

Mutations in the acid beta-glucuronidase gene lead to systemic accumulation of undegraded glycosaminoglycans in lysosomes and ultimately to clinical manifestations of mucopolysaccharidosis VII (Sly disease). Gene transfer by retrovirus vectors into murine mucopolysaccharidosis VII hematopoietic stem cells or fibroblasts ameliorates glycosaminoglycan accumulation in some affected tissues. The efficacy of gene therapy for mucopolysaccharidosis VII depends on the levels of beta-glucuronidase secreted by gene-corrected cells; therefore, enrichment of transduced cells expressing high levels of enzyme prior to transplantation is desirable. We describe the development of a fluorescence-activated cell sorter-based assay for the quantitative analysis of beta-glucuronidase activity in viable cells. Murine mucopolysaccharidosis VII cells transduced with a beta-glucuronidase retroviral vector can be isolated by cell sorting on the basis of beta-glucuronidase activity and cultured for further use. In vitro analysis revealed that sorted cells have elevated levels of beta-glucuronidase activity and secrete higher levels of cross-correcting enzyme than the population from which they were sorted. Transduced fibroblasts stably expressing beta-glucuronidase after subcutaneous passage in the mucopolysaccharidosis VII mouse can be isolated by cell sorting and expanded ex vivo. A relatively high percentage of these cells maintain stable expression after secondary transplantation, yielding significantly higher levels of enzymatic activity than that generated in the primary transplant.

In vivo migration and function of transferred HIV-1-specific cytotoxic T cells

The persistence of HIV replication in infected individuals may reflect an inadequate host HIV-specific CD8+ cytotoxic T lymphocyte (CTL) response. The functional activity of HIV-specific CTLs and the ability of these effector cells to migrate in vivo to sites of infection was directly assessed by expanding autologous HIV-1 Gag-specific CD8+ CTL clones in vitro and adoptively transferring these CTLs to HIV-infected individuals. The transferred CTLs retained lytic function in vivo, accumulated adjacent to HIV-infected cells in lymph nodes and transiently reduced the levels of circulating productively infected CD4+ T cells. These results provide direct evidence that HIV-specific CTLs target sites of HIV replication and mediate antiviral activity, and indicate that the development of immunotherapeutic approaches to sustain a strong CTL response to HIV may be a useful adjunct to treatment of HIV infection.

Generation of retroviral vector for clinical studies using transient transfection

Transient transfection of 293T cells was utilized to produce high-titer murine recombinant retroviral vectors for clinical studies. This system was initially optimized by gene transfer using different retroviral envelope proteins into activated human CD4+ T lymphocytes in vitro. Higher titer and infectivity were obtained than with stable murine producer lines; titers of 0.3-1 x 10(7) infectious units per milliliter for vectors encoding the green fluorescent protein (GFP) were achieved. Virions pseudotyped with envelope proteins from gibbon ape leukemia virus or amphotropic murine leukemia virus resulted in gene transfer of > or = 50% in CD4+ human T lymphocytes with this marker. Gene transfer of Rev M10 with this vector conferred resistance to HIV infection compared with negative controls in the absence of drug selection. Thus, the efficiency of transduction achieved under these conditions obviated the need to include selection to detect biologic effects in T cells. Finally, a protocol for the production of large-scale supernatants using transient transfection was optimized up to titers of 1.9 x 10(7) IU/ml. These packaging cells can be used to generate high-titer virus in sufficient quantities for clinical studies and will facilitate the rapid, cost-effective generation of improved retroviral, lentiviral, or other viral vectors for human gene therapy.

Identification of gp100-derived, melanoma-specific cytotoxic T-lymphocyte epitopes restricted by HLA-A3 supertype molecules by primary in vitro immunization with peptide-pulsed dendritic cells

The human melanocyte lineage-specific antigen gp100 contains several epitopes recognized by cytotoxic T lymphocytes (CTL). However, most of the epitopes reported to date are HLA-A2.1-restricted. Despite the high frequency of HLA-A2.1 in melanoma patients, effective population coverage requires the identification of epitopes restricted by other frequent HLA alleles. Herein, HLA-A3 binding, gp100-derived synthetic peptides were tested for their capacity to elicit anti-melanoma CTL in vitro using CD8+ T cells from healthy donors as responders and peptide-pulsed autologous dendritic cells as antigen-presenting cells. Of 7 peptides tested, 2 (gp100[9(87)] and gp100[10(86)]) induced CTLs that killed melanoma cell lines expressing HLA-A3 and gp100. Additional MHC-binding studies to various HLA molecules belonging to the HLA-A3 superfamily (HLA-A*1101, -A*3101, -A*3301 and -A*6801) were performed to determine whether these CTL epitopes could further increase potential population coverage. Further experiments indicated that the peptide gp100[9(87)], which bound to HLA-A11 with high affinity, was capable of inducing specific CTLs that killed melanoma cells expressing gp100 and HLA-A11 molecules. Our results indicate that the gp100[9(87)] peptide corresponds to a CTL epitope which may be restricted by either the HLA-A3 or HLA-A11 allele, emphasizing its utility for the design and development of epitope-based therapies for melanoma.

Rapid retroviral infection of human haemopoietic cells of different lineages: efficient transfer in fresh T cells

In order to develop a clinically feasible gene marking approach, we have used the recently described PINCO retroviral expression system, composed of the enhanced green fluorescence protein (EGFP) cDNA driven by Moloney MLV LTR and packaged in the Phoenix amphotropic cell line. Two T, five B, one erythromyeloid and three myeloid cell lines were successfully infected with % GFP+ cells ranging from 4% to 79%, showing a lineage-dependent difference in infection susceptibility, with the myeloid cells being the least efficiently infected. We also infected normal mononuclear peripheral cells cultured in PHA and rhIL-2 for 2 d, and obtained an average of 30% GFP+ cells, all present within the CD3+ population, with CD4+ and CD8+ cells being equally infected. Finally, the tonsillar purified B population showed lower levels of infectivity (6%) whereas high susceptibility was shown by normal human umbilical vein endothelial cells (57%). Highly purified CD34+ cells were also susceptible, varying from 6% to 10% GFP+ cells. Immature myeloid/erythroid progenitors have been infected which stably expressed the GFP protein during further differentiation in culture. The GFP+ T cells were FACS-sorted rapidly upon infection, subsequently cultured and the fluorescence intensity monitored. In all cases the difference in percentage of GFP+ cells did not correlate with the percentage of S/G2/M cycling cells as determined at the moment of infection or with the expression levels of Ram-1 amphotrophic receptor. The improved safety of this retroviral system, the rapidity of the technique, the high efficiency of infection with respect to normal T lymphocytes (in this last case higher than previously reported) and the lack of need for in vitro selection make this system favourable for clinical development.

Herpes simplex virus thymidine kinase gene transfer for controlled graft-versus-host disease and graft-versus-leukemia: clinical follow-up and improved new vectors

We previously demonstrated that severe graft-versus-host disease (GvHD), associated with the therapeutic infusion of donor lymphocytes after allogeneic marrow transplantation (BMT), can be efficiently controlled by the SFCMM-2-mediated expression of the herpes simplex virus thymidine kinase (HSV-tk) suicide gene into the allogeneic lymphocytes. This was achieved by selective elimination of transduced lymphocytes by ganciclovir (GCV) infusion. Despite the positive results of the pilot clinical trial, two vector-related limitations were observed. The induction of a strong immune response against genetically modified cells was observed in two patients. In addition, the only patient who developed chronic GvHD showed only partial response to ganciclovir treatment. In an attempt to overcome these limitations, we developed a new generation of vectors. The neomycin resistance (neoR) gene was removed from the SFCMM-3 and SFCMM-4 retroviral vectors. These vectors are less immunogenic and able to confer higher ganciclovir sensitivity to transduced human lymphocytes. All the vectors carry a modified form of the low-affinity nerve growth factor receptor cDNA, as cell surface selectable marker (deltaLNGFR). The vectors were compared in terms of gene transfer efficiency, and ability to confer high and specific sensitivity to ganciclovir. The SFCMM-3 vector, carrying the entire HSV-tk gene driven by the LTR promoter, allows efficient transduction of human T lymphocytes and confers the highest GCV sensitivity to transduced lymphocytes with a high and a low proliferation index. The expression of the deltaLNGFR marker allows an easier in vitro manipulation and a faster immune selection of transduced cells compared with neoR selection. Finally, the elimination of the neoR gene removes a potent immunogen from transduced lymphocytes.

Genetic vaccination-induced immune responses to the human immunodeficiency virus protein Rev: emergence of the interleukin 2-producing helper T lymphocyte

Rev M10 is a trans-dominant negative inhibitor of HIV replication. Hence, stable transduction of CD4+ T cells with Rev M10 represents a novel gene therapy aimed at inhibiting HIV replication within these cells, thereby slowing the progression of AIDS. However, the immune system may recognize Rev M10 as foreign and target transduced cells for elimination. In the current study, mice were genetically immunized with a plasmid encoding Rev M10, to (1) identify immune parameters that may be induced by Rev M10 gene transfer, (2) determine the impact of repeated introduction of the Rev M10-encoding plasmid on the immune response to the transgene product, and (3) determine if cotransfection with a plasmid encoding TGFbeta1 would suppress the response. Kinetic studies revealed that Rev-specific IL-2-producing helper T lymphocytes (HTLs) appeared following the second genetic immunization, peaked after the third, and persisted at peak levels for at least 6 weeks. Rev-specific HTLs were CD4+, and the development of these cells was ablated by cotransfection with TGFbeta1. Other cytokines were not readily detectable when immune splenocytes were restimulated with Rev in vitro, and Rev-specific IgG antibodies were not present in the sera of these mice. To our knowledge, this represents the first report that genetic immunization with Rev M10 induces an immune response that is dominated by IL-2-producing HTLs. Further, this study demonstrates the potential utility of introducing immunosuppressive genes as a means to control the immune response to foreign transgene products.

Large-scale production of CD4+ T cells from HIV-1-infected donors after CD3/CD28 costimulation

We describe a procedure for large-scale enrichment, growth, and harvesting CD4+ T cells. This method may be effective for HIV-1 immunotherapy, as the mode of stimulation, with anti-CD3 plus anti-CD28 coated beads (CD3/CD28 beads) induces a potent antiviral effect. PBMC were obtained by density gradient centrifugation of an apheresis product. Monocytes/macrophages were removed by incubating PBMC with beads coated with IgG. The cells were then magnetically depleted of B cells and CD8+ cells with mouse anti-CD20 and anti-CD8 MAbs and sheep antimouse coated beads. The remaining cells were >80% CD4+ and were transferred to gas-permeable bags containing CD3/CD28 beads and cultured in a closed system. After 14 days, the cell number increased an average of 37-fold, and cells were nearly 100% CD4+. Viral load, assessed by DNA PCR for HIV-1 gag, decreased >10-fold during culture in the absence of antiretroviral agents. Removal of CD3/CD28 beads from the cell suspension was accomplished by passing cells plus beads (3-30 x 10(9) cells in 2-12 L) over a MaxSep magnetic separator using gravity-driven flow. The cells were then concentrated to 300 ml in an automated centrifuge. This process allows safe and efficient growth of large numbers of CD4+ T cells from HIV-1+ donors.

Expression of the activation antigen CD69 predicts functionality of in vitro expanded peripheral blood mononuclear cells (PBMC) from healthy donors and HIV-infected patients

Gene therapy for AIDS necessitates harvest and expansion of PBMC from HIV-infected patients. We expanded PBMC from healthy blood donors and HIV-infected patients for up to 14 days using four expansion protocols: 3 days of phytohaemagglutinin (PHA) stimulation, continuous PHA stimulation, 3 days of stimulation with anti-CD3 and anti-CD28, and continuous stimulation with anti-CD3 and anti-CD28. Functionality of PBMC was evaluated prior to and after expansion using standard proliferation assay. Phenotype and lymphocyte subset activation defined by expression of CD69 and CD25 were determined using flow cytometry. PBMC from healthy donors and HIV-infected patients were readily expanded. The best expansion was obtained using stimulation for 3 days. After expansion, functionality of PBMC measured as proliferative response was partly conserved. PBMC expanded with stimulation for 3 days exhibited more preserved functionality than PBMC stimulated continuously (P < 0.03). The mean proliferative response in each of the four different expansion protocols correlated with the mean values of CD69 expression. The proliferative responses from patients and healthy donors expanded with PHA stimulation for 3 days correlated with CD69 expression on CD4 cells (r = 0.68, P < 0.01) and on CD8 cells (r = 0.59, P < 0.03). Furthermore, expression of CD69 reliably predicted which patients and donors had highly conserved functionality after in vitro expansion. Finally, PBMC expanded with PHA stimulation for 3 days were examined for apoptosis. Only a minor fraction was primed for apoptosis, and this fraction could be significantly reduced by addition of IL-2 to the culture medium (P < 0.05). In conclusion, the feasibility of expanding PBMC from HIV patients was demonstrated. Expanded PBMC had conserved functionality. Finally, after in vitro expansion, expression of the activation antigen CD69 reliably predicted functionality of PBMC.

Impact of preexisting and induced humoral and cellular immune responses in an adenovirus-based gene therapy phase I clinical trial for localized mesothelioma

Little is known about the immune responses induced by recombinant adenoviral (Ad) vectors in humans. The humoral and cellular immune responses were therefore analyzed in 21 patients with localized malignancy (mesothelioma), who received intrapleurally high doses of a replication-defective Ad5 vector carrying a suicide gene. Eight of 21 patients had pretreatment titers of neutralizing antibodies (NAb) to Ad at > or =1:100. Peripheral blood mononuclear cells (PBMCs) proliferated in response to adenoviral 5 structural proteins before treatment in 17 of 21 patients. Preexisting humoral and cellular immunity did not preclude gene transfer. Vector instillation induced high titers of nonneutralizing and neutralizing anti-Ad antibody (4- to 341-fold increase in 18 of 20 patients) in a dose-dependent manner. Three patients generated antibodies to the transgene, herpes simplex virus thymidine kinase. Ad5-specific proliferation of PBMCs increased significantly (>3-fold) after vector administration in 12 of 21 patients in a dose-dependent manner. Thus, replication-defective Ad5 administered intrapleurally induced significant humoral and cellular immune responses that induced no obvious adverse clinical sequelae.

Anti-HIV type 1 activity of wild-type and functional defective RANTES intrakine in primary human lymphocytes

We have developed a genetic "intrakine" strategy to inactivate the CC-chemokine receptor 5 (CCR-5), the principal coreceptor for macrophage (M)-tropic HIV-1 viruses (Yang et al, 1997). The inactivation of CCR5 was achieved by targeting a modified CC-chemokine (RANTES) to the lumen of the endoplasmic reticulum (ER) to block the transport of the newly synthesized CCR-5. The transduced lymphocytes with the phenotypic CCR5 knockout were shown to be resistant to M-tropic HIV-1 infection. This study illustrated the feasibility of the intrakine strategy to block HIV-1 infection. In our current study, the potential clinical application of the intrakine approach was further evaluated in human peripheral blood lymphocytes (PBLs). PBLs were transduced with the RANTES intrakine gene by using retroviral vectors with the truncated low-affinity human nerve growth factor receptor (deltaNGFR) marker, and then isolated by an anti-NGFR antibody/magnetic bead method. The surface expression of CCR-5 in the transduced lymphocytes was dramatically inhibited, as demonstrated by flow cytometric assays. The transduced PBLs were shown to resist various types of M-tropic HIV-1 virus infection. The cell viability, cell proliferation rates, and cell surface markers of the intrakine-transduced PBLs were shown to be comparable to those of control PBLs. The transduced PBLs were also found to respond to the stimulation of various CXC- and CC-chemokines, other than RANTES. The transduced PBLs responded to tetanus antigen stimulation by increasing IL-2 production and cell proliferation. In addition, a functionally defective mutant of RANTES that retains its binding activity to CCR-5, but loses its signaling ability, was used to generate a mutant RANTES intrakine. The primary lymphocytes transduced with the mutant RANTES intrakine were found to be resistant to M-tropic HIV-1 infection. From these results, we conclude that the primary human lymphocytes transduced with either the wild-type or functionally defective RANTES intrakine are resistant to M-tropic HIV-1 infection, and maintain their basic biological functions. This study, therefore, indicates the potential clinical application of the intrakine approach for HIV-1 gene therapy.

Retroviral Marking of Canine Bone Marrow: Long-Term, High-Level Expression of Human Interleukin-2 Receptor Common Gamma Chain in Canine Lymphocytes

Optimization of retroviral gene transfer into hematopoietic cells of the dog will facilitate gene therapy of canine X-linked severe combined immunodeficiency (XSCID) and in turn advance similar efforts to treat human XSCID. Both canine and human XSCID are caused by defects in the common γ chain, γc, of receptors for interleukin-2 and other cytokines. In this study, normal dogs were given retrovirally transduced bone marrow cells with and without preharvest mobilization by the canine growth factors granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF). Harvey sarcoma virus and Moloney murine leukemia virus constructs were used, both containing cDNA encoding human γc. The Harvey-based vector transduced into cytokine-primed marrow yielded persistent detectable provirus in bone marrow and blood and expression of human γc on peripheral lymphocytes. In three dogs, human γc expression disappeared after 19 to 34 weeks but reappeared and was sustained, in one dog beyond 16 months posttransplantation, upon immunosuppression with cyclosporin A and prednisone, with up to 25% of lymphocytes expressing human γc. The long-term expression of human γc in a high proportion of normal canine lymphocytes predicts that retrovirus-mediated gene correction of hematopoietic cells may prove to be of clinical benefit in humans affected with this XSCID.

This is a US government work. There are no restrictions on its use.

Retroviral Marking of Canine Bone Marrow: Long-Term, High-Level Expression of Human Interleukin-2 Receptor Common Gamma Chain in Canine Lymphocytes

Optimization of retroviral gene transfer into hematopoietic cells of the dog will facilitate gene therapy of canine X-linked severe combined immunodeficiency (XSCID) and in turn advance similar efforts to treat human XSCID. Both canine and human XSCID are caused by defects in the common γ chain, γc, of receptors for interleukin-2 and other cytokines. In this study, normal dogs were given retrovirally transduced bone marrow cells with and without preharvest mobilization by the canine growth factors granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF). Harvey sarcoma virus and Moloney murine leukemia virus constructs were used, both containing cDNA encoding human γc. The Harvey-based vector transduced into cytokine-primed marrow yielded persistent detectable provirus in bone marrow and blood and expression of human γc on peripheral lymphocytes. In three dogs, human γc expression disappeared after 19 to 34 weeks but reappeared and was sustained, in one dog beyond 16 months posttransplantation, upon immunosuppression with cyclosporin A and prednisone, with up to 25% of lymphocytes expressing human γc. The long-term expression of human γc in a high proportion of normal canine lymphocytes predicts that retrovirus-mediated gene correction of hematopoietic cells may prove to be of clinical benefit in humans affected with this XSCID.

This is a US government work. There are no restrictions on its use.

Redesigning an FKBP-ligand interface to generate chemical dimerizers with novel specificity

FKBP ligand homodimers can be used to activate signaling events inside cells and animals that have been engineered to express fusions between appropriate signaling domains and FKBP. However, use of these dimerizers in vivo is potentially limited by ligand binding to endogenous FKBP. We have designed ligands that bind specifically to a mutated FKBP over the wild-type protein by remodeling an FKBP-ligand interface to introduce a specificity binding pocket. A compound bearing an ethyl substituent in place of a carbonyl group exhibited sub-nanomolar affinity and 1,000-fold selectivity for a mutant FKBP with a compensating truncation of a phenylalanine residue. Structural and functional analysis of the new pocket showed that recognition is surprisingly relaxed, with the modified ligand only partially filling the engineered cavity. We incorporated the specificity pocket into a fusion protein containing FKBP and the intracellular domain of the Fas receptor. Cells expressing this modified chimeric protein potently underwent apoptosis in response to AP1903, a homodimer of the modified ligand, both in culture and when implanted into mice. Remodeled dimerizers such as AP1903 are ideal reagents for controlling the activities of cells that have been modified by gene therapy procedures, without interference from endogenous FKBP.

Canine T cells transduced with a herpes simplex virus thymidine kinase gene: a model to study effects on engraftment and control of graft-versus-host disease

BACKGROUND

Alloreactive donor T cells in marrow grafts mediate graft-versus-host disease (GVHD), but T-cell depletion has resulted in increased graft failure. Add-back of gene-modified alloreactive donor T cells could prevent graft rejection. After engraftment, in vivo depletion of those modified T cells with ganciclovir may control GVHD.

METHODS

Canine recipient-specific donor cytotoxic T lymphocytes (CTL) were retrovirally transduced with the herpes simplex virus thymidine kinase gene.

RESULTS

Gibbon ape leukemia virus-pseudotyped vector yielded primary CTL transduction efficiency of 22.9+/-9.9%. After selection and expansion, 96.7+/-0.8% of CTL expressed retrovirally transferred genes. Recipient-specific cytotoxic activity was maintained with 84.3% specific lysis. After ganciclovir treatment, herpes simplex virus thymidine kinase-transduced CTL proliferation was reduced 98.7+/-0.2% compared with controls.

CONCLUSIONS

We have demonstrated efficient ex vivo transduction, expansion, maintenance of alloreactivity, and ganciclovir-mediated ablation of canine CTL, which will permit in vivo studies in the dog, a well-established model for GVHD and engraftment.

Gene and cell transfer for specific immunotherapy

The realisation that human tumor cells may express and process tumor specific and tumor associated antigens has increased interest in immunotherapeutic approaches to cancer treatment. This interest has been coupled with a burgeoning ability to genetically modify tumor cells and components of the immune system, in an effort to maximize the anti-neoplastic response. In a number of settings, gene modified tumor vaccines, cytotoxic T cells and dendritic cells are producing both immunomodulation and clinically evident benefits. Continued exploration of this approach seems well justified.

Stomach Implant for Long-Term Erythropoietin Expression in Rats

To approach the goal of consistent long-term erythropoietin (Epo) expression in vivo, we developed an implantation procedure in which transduced autologous vascular smooth muscle was introduced into rats in a chamber created from a polytetrafluoroethylene (PTFE) ring placed under the serosa of the stomach. The implant became vascularized and permitted the long-term survival of smooth muscle cells expressing Epo. Hematocrits of treated animals increased rapidly and monitored over 12 months gave a mean value of 56.0 ± 4.0% (P < .001; n = 9), increased from a presurgery mean of 42.3 ± 1.6%. Hemoglobin levels rose from a presurgery mean of 15.2 ± 0.4 g/dL and for 12 months were significantly elevated with a mean value of 19.5 ± 1.3 g/dL (P < .001; n = 9). The hematocrit and hemoglobin levels of control animals receiving human adenosine deaminase (ADA)–expressing cells were not significantly different from baseline (P > .05; n = 5). In response to tissue oxygenation, kidney, and (to a lesser extent) liver are specific organs that synthesize Epo. Treated animals showed downregulation of endogenous Epo mRNA in kidney over a 12-month period. The PTFE implant provides sustained gene delivery, is safe, and is minimally invasive. It allows easy engraftment of transduced cells and may be applied generally to the systemic delivery of therapeutic proteins such as hormones and clotting factors.

© 1998 by The American Society of Hematology.

Spontaneous silencing of humanized green fluorescent protein (hGFP) gene expression from a retroviral vector by DNA methylation

We have constructed a functional murine leukemia virus (MLV)-derived retroviral vector transducing two genes encoding the autofluorescent humanized green fluorescent protein (hGFP) and neomycin phosphotransferase (Neo). This was done to determine whether hGFP could function as a marker gene in a retroviral vector and to investigate the expression of genes in a retroviral vector. Surprisingly, clonal vector packaging cell lines showed variable levels of hGFP expression, and expression was detected in as few as 49% of the cells in a clonally derived culture. This indicated that hGFP expression was silenced in individual cells. This silencing could be diminished by selective culturing of the vector packaging cells with the neomycin analog G418 and was reduced by a 3-day treatment with the demethylating agent 5-azacytidine. The 5-azacytidine effect was transient, and hGFP expression in the vector packaging cells returned to untreated control levels within 2 weeks. Using flow cytometric analysis, hGFP expression was detected in up to 15% of transduced MT4 cells (a CD4+ lymphocytic cell line) after coculturing with packaging cells for 4 days. A 3-day postcoculture treatment with 5-azacytidine was shown to increase the hGFP-expressing MT4 cells from either 10.4% to 11.6% or 3.7% to 4.8%, corresponding to an increase in observed transduction efficiencies of 12% and 30%, respectively. These results indicate that silencing of gene expression from a retroviral vector may result from DNA methylation and occurs rapidly after transduction.

Stomach Implant for Long-Term Erythropoietin Expression in Rats

To approach the goal of consistent long-term erythropoietin (Epo) expression in vivo, we developed an implantation procedure in which transduced autologous vascular smooth muscle was introduced into rats in a chamber created from a polytetrafluoroethylene (PTFE) ring placed under the serosa of the stomach. The implant became vascularized and permitted the long-term survival of smooth muscle cells expressing Epo. Hematocrits of treated animals increased rapidly and monitored over 12 months gave a mean value of 56.0 ± 4.0% (P &lt; .001; n = 9), increased from a presurgery mean of 42.3 ± 1.6%. Hemoglobin levels rose from a presurgery mean of 15.2 ± 0.4 g/dL and for 12 months were significantly elevated with a mean value of 19.5 ± 1.3 g/dL (P &lt; .001; n = 9). The hematocrit and hemoglobin levels of control animals receiving human adenosine deaminase (ADA)–expressing cells were not significantly different from baseline (P &gt; .05; n = 5). In response to tissue oxygenation, kidney, and (to a lesser extent) liver are specific organs that synthesize Epo. Treated animals showed downregulation of endogenous Epo mRNA in kidney over a 12-month period. The PTFE implant provides sustained gene delivery, is safe, and is minimally invasive. It allows easy engraftment of transduced cells and may be applied generally to the systemic delivery of therapeutic proteins such as hormones and clotting factors.

© 1998 by The American Society of Hematology.

Peripheral expansion of pre-existing mature T cells is an important means of CD4+ T-cell regeneration HIV-infected adults

The CD4+ T-cell pool in HIV-infected patients is in a constant state of flux as CD4+ T cells are infected and destroyed by HIV and new cells take their place. To study T-cell survival, we adoptively transferred peripheral blood lymphocytes transduced with the neomycin phosphotransferase gene between syngeneic twin pairs discordant for HIV infection. A stable fraction of marked CD4+ T cells persisted in the circulation for four to eighteen weeks after transfer in all patients. After this time there was a precipitous decline in marked cells in three of the patients. At approximately six months, marked cells were in lymphoid tissues in proportions comparable to those found in peripheral blood. In two patients, the proportion of total signal for the transgene (found by PCR analysis) in the CD4/CD45RA+ T-cell population relative to the CD4/CD45RO+ population increased in the weeks after cell infusion. These findings indicate that genetically-marked CD4+ T cells persist in vivo for weeks to months and that the CD4+ T-cell pool in adults is maintained mostly by the division of mature T cells rather than by differentiation of prethymic stem cells. Thus, after elements of the T-cell repertoire are lost through HIV infection, they may be difficult to replace.

Adenovirus vectors as transcomplementing templates for the production of replication defective retroviral vectors

We have generated an adenovirus containing a retroviral vector sequence encoding the neomycin phosphotransferase (neo) gene (AV-LXSN). AV-LXSN transduction of retroviral packaging cell lines led to production of LXSN retroviral vector with alternative viral envelopes; exposure of target cells to retroviral containing supernatants confirmed envelope specific tropism. Retroviral titers (G418 cfu/ml) were comparable to those produced by standard techniques. Retrovirus could be detected in supernatants within 24 hours of AV-LXSN transduction and persisted as long as 120 hours. Southern blot analysis of DNA purified from populations of G418 cells showed the presence of a single neo containing restriction fragment of the appropriate size that could only be generated by reverse transcription of LXSN to produce LXSN provirus. This adeno-retroviral chimeric vector system could simplify the generation and testing of different retroviral vectors, particularly where assessment of vectors with alternative envelopes carrying novel targeting ligands is required.

Sustained expression of high levels of human factor IX from human cells implanted within an immunoisolation device into athymic rodents

Immunoisolation of allogeneic cells within a membrane-bound device is a unique approach for gene therapy. We employed an immunoisolation device that protects allograft, but not xenograft, cells from destruction, to implant a human fibroblast line (MSU 1.2) in athymic rodents. Cells, transduced with the MFG-human factor IX retroviral vector, and expressing 0.9 microg/10(6) cells/day in vitro, were implanted in rats (four 40-microl devices, each containing 2 x 10(7) cells, two subcutaneously, two in epididymal fat) and in mice (two 20-microl devices, each containing 2 x 10(6) cells, subcutaneously). Plasma factor IX levels increased for 50 days, reaching maxima of 203 ng/ml (rat) and 597 ng/ml (mouse), and both continued at greater than 100 ng/ml for more than 140 days. A clone derived from the transduced cells, making 5 microg of factor IX/10(6) cells/day, was implanted within a device (one 20-microl device containing 2.5 x 10(6) cells), or without a device (1 x 10(7) cells implanted freely), either subcutaneously or in epididymal fat. The freely implanted cells expressed transiently, reaching more than 100 ng/ml in each site by day 4, but dropped to zero by day 20 (subcutaneous) or day 90 (epididymal fat). In devices, levels gradually increased to 100 ng/ml (subcutaneous) or 300 ng/ml (epididymal fat), remaining high for more than 100 days. These results show long-term, high-level expression of a human protein: (1) when cells are implanted within a cell transplantation device, but not when the cells are freely implanted, and (2) from a transgene driven by a viral promoter. An alloprotective device will enable the use of cloned cell lines that can be subjected to stringent quality control assessment that is impossible to achieve with autologous approaches.

Controlling gene expression using synthetic ligands

Chemical inducers of dimerization (dimerizers) are a new class of reagents used for controlling protein-protein interactions. Use of a small-molecule, cell-permeable dimerizer to control the interaction of a transcription activation domain and a DNA-binding domain allows the level of expression of a target gene to be regulated by the concentration of dimerizer. The modular design of components has facilitated the development of multiple systems that can be used to readily generate cell lines in which basal expression of the target gene is low and induced to high levels by a nontoxic dimerizer. The development and use of one such system to control the expression of a gene in cultured cells are described.

Development of improved adenosine deaminase retroviral vectors

A series of adenosine deaminase (ADA) retroviral vectors were designed and constructed with the goal of improved performance over the PA317/LASN vector currently used in clinical trials. First, the bacterial selectable-marker neomycin phosphotransferase (neo) gene was removed to create a "simplified" vector. Second, the Moloney murine leukemia virus long terminal repeat (LTR) promoter used for ADA expression was replaced with either the myeloproliferative sarcoma virus (MPSV) or SL3-3 LTR. Supernatant from each ADA vector was used to transduce ADA-deficient (ADA-) B- and T-cell lines as well as primary peripheral blood mononuclear cells (PBMC) from an ADA- severe combined immunodeficiency patient. Total ADA enzyme activity and ADA activity per integrant in the transduced cells demonstrated that the MPSV LTR splicing vector design provided the highest level of ADA expression per cell. This ADA(MPSV) vector was then tested in packaging cell lines containing either the gibbon ape leukemia virus envelope (PG13 cells), the murine amphotropic envelope (FLYA13 cells), or the feline endogenous virus RD114 envelope (FLYRD18 cells). The results indicate that FLYRD18/ADA(MPSV), a simplified ADA retroviral vector with the MPSV LTR, provides a 17-fold-higher level of ADA expression in human lymphohematopoietic cells than the PA317/LASN vector currently in use.

Enhanced T cell engraftment after retroviral delivery of an antiviral gene in HIV-infected individuals

Intracellular expression of gene products that inhibit viral replication have the potential to complement current antiviral approaches to the treatment of AIDS. We previously have shown that a mutant inhibitory form of an essential viral protein, Rev M10, prolongs the survival of T cells transduced with a nonviral vector in HIV-infected individuals. Because these gene-modified cells were not observed in patients beyond 8 weeks, efforts were made to improve the duration of engraftment. In this study, we used retroviral vector delivery of Rev M10 to CD4(+) cells and analyzed relevant immune responses in a pilot study of three HIV-seropositive patients. DNA and RNA PCR analyses revealed that cells transduced with Rev M10 retroviral vectors survived and expressed the recombinant gene for significantly longer time periods than those transduced with a negative control vector in all three patients. Immune responses were not detected either to Rev M10 or to Moloney murine leukemia virus gp70 envelope protein. Rev M10-transduced cells were detected for an average of 6 months after retroviral gene transfer compared with approximately 3 weeks for the previously reported nonviral vector delivery. These findings suggest that retroviral delivery of an antiviral gene may potentially contribute to immune reconstitution in AIDS and could provide a more effective vector to prolong survival of CD4(+) cells in HIV infection.